fix invalid boolean conversion

[grosser]

dir += '/' if not (dir.empty? or dir.end_with? '/')
is not the same as
dir += '/' if not dir.empty? or dir.end_with?('/')

530dac2

@clarete

[grosser]

please release a new patch version after merging that

[clarete]

This is the kind of bug that I cause when I don't write enough tests :/

I'll definitely have to increase the test coverage of this tool soon. About the new release, there's something else I wanna push, but I'll definitely release a new version tonight.

Thank you again for your awesome work.